Transmission Electron
Microscopy
Nano Measurement
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Measurements involve bombardment of particles on samples (i-e, Photon, Ions,
Electrons)
Depending on nature of bombardment particle different information can be
obtained
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Size
Element composition
Crystallinity, Molecular Structure
Physical Properties
Electron as a Source
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Optical Microscope, visible light is used as a source
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Resolution: few microns – 100 microns
For imaging of nanomaterials, electrons are used as instead of light
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Resolution: few nanometer – few microns
Resolution of Microscope depends on wavelength (Rayleigh Eq)
0.6 𝜆
𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =
𝑁𝑢𝑚𝑒𝑟𝑖𝑐𝑎𝑙 𝐴𝑝𝑒𝑟𝑡𝑢𝑟𝑒
We can change the resolution of Electron microscope by changing accelerating
voltage, which changes the velocity, which in turn changes wavelength associated
with electron
Electron as bombardment particle
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Electron bombarded on sample they are either
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Capture by sample
Scattered back
Knock out electrons already present in sample
Transmitted through the sample
If sample thickness is less than 100 nm, electron can pass through the material and
scattered either elastically or inelastically giving information about Crystallinity
and atomic concentration
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They are used in transmission electron microscopy
Transmission Electron Microscope
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Use for nanoscale imaging, ~ 0.5 nm
Small temperature fluctuations can cause noise in images
Operated in highly controlled environments
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Operated in basements
Floating tables
Radiative cooling panels
Complementary Measurements
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Electron diffraction :
Information about crystal structure
Electron Energy loss spectroscopy:
Information about atomic concentrations
Transmission Electron Microscope
Sample Requirement
• Since working is based on transmitted electrons from the sample
• Samples should be very thin ~ 100 nm
• Specials methods are used to prepare sample
Sample before polishing
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Mechanical Polishing
Laser / Ion beam milling
Sample after polishing
Sample Requirements
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TEM Grid
Metallic Samples
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Mechanical Polishing using abrasive paper
Samples are polished in wedge shape
Further, thinning is done by highly accelerated Ar ions falling on the sample and removing
material physically
Samples are then place on TEM grids
Nanomaterial, Powdered Sample
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Dispersed in Solvents (Ethanol)
Add drops on TEM grids and dry
Drawbacks
• 2D imaging
• Artifacts leads to misinterpretation of results
• Small volume of samples is imaged
• Aberration in EM Lenses leads to distorted images
• Always complement TEM images with a surface imaging technique
Graphene
Top View
Cross Section
View
Multiwalled Carbon Nanotube
Different Morphology of Gold Nanoparticles
Ferrite Nanoparticles attached with CNTs
Lead Selenide Nanoparticles
Diffraction pattern , grains, grains boundaries of Palladium
Electron Diffraction of FCC Steel